This invention relates to an induction furnace for use in melting or processing a material, such as used dry batteries (abbreviated to UDB), electric arc furnace dust (EFD), activated sludge burned ashes (ASA), ashes of garbage incineration, and the like. It is to be noted that such a material to be processed will be simply called a material hereinunder.
In general, an induction furnace of the type described comprises a crucible for charging or dumping a material to be processed and a coil member wound around the crucible. An a.c. exciting current of a low frequency, for example, 50-60 Hz is caused to flow from an a.c. current source through the coil member to induce an electromagnetic flux within the crucible. As a result, an eddy-current flows in the material which is charged into the crucible through an inlet port. The material is heated by the eddy-current within the crucible. Thus, induction heating is carried out in the crucible. In this event, the material is agitated to be fused and is sent through an outlet port in the form of a slag or a molten bath.
In the induction furnace for the present purpose, it is preferable that each of charged materials is heated from the inlet port to the outlet port for a uniform retention time. Otherwise, a uniform slag and metal product can not be ejected through the outlet port.
However, it has been pointed out that such a retention time is often variable for the materials in the conventional induction furnace.
In order to prevent such variation of the retention time, proposal has been made in Japanese Utility Model Publication No. Syo 64-558, namely, 558/1989 about an induction furnace comprising a crucible which has a crucible center axis and an axial symmetrical configuration with respect to the crucible center axis. Specifically, the crucible is outlined by an inverted frustum contour, namely, an inverted circular truncated contour. An induction coil is wound around the crucible so that the crucible center axis becomes a winding axis. In addition, it is assumed that the inlet and the outlet ports are located on both sides of the crucible center axis and are adjacent to the crucible side wall as compared with the crucible center axis. Under the circumstances, when the material is charged into the crucible through the inlet port adjacent to the crucible side wall, a temperature of the slag bath is locally lowered at an area near to the inlet port. As a result, a temperature of the crucible side wall is also locally lowered at a position adjacent to the low temperature area of the slag bath. The charged material is liable to be adhered to such a low temperature position of the crucible side wall.